Zuerch Lab
ULTRAFAST MATERIALS CHEMISTRY AT BERKELEY
Zuerch Lab
ULTRAFAST MATERIALS CHEMISTRY AT BERKELEY

News
New paper out: Mechanistic Investigation, Wavelength-Dependent Reactivity, and Expanded Reactivity of N–Aryl Azacycle Photomediated Ring Contractions
Feb 21 2024

Under mild blue-light irradiation, α-acylated saturated heterocycles undergo a photomediated one-atom ring contraction that extrudes a heteroatom from the cyclic core. However, for nitrogenous heterocycles, this powerful skeletal edit has been limited to substrates bearing electron-withdrawing substituents on nitrogen. Moreover, the mechanism and wavelength-dependent efficiency of this transformation have remained unclear. In our most recent joint work between organic chemistry and photochemistry, we increased the electron richness of nitrogen in saturated azacycles to improve light absorption and strengthen critical intramolecular hydrogen bonding while enabling the direct installation of the photoreactive handle. As a result, a broadly expanded substrate scope, including underexplored electron-rich substrates and previously unsuccessful heterocycles, has now been achieved. The significantly improved yields and diastereoselectivities have facilitated reaction rate, kinetic isotope effect (KIE), and quenching studies, in addition to the determination of quantum yields. Guided by these studies, we propose a revised ET/PT mechanism for the ring contraction, which is additionally corroborated by computational characterization of the lowest-energy excited states of α-acylated substrates through time-dependent DFT. The efficiency of the ring contraction at wavelengths longer than those strongly absorbed by the substrates was investigated through wavelength-dependent rate measurements, which revealed a red shift of the photochemical action plot relative to substrate absorbance. The elucidated mechanistic and photophysical details effectively rationalize empirical observations, including additive effects, that were previously poorly understood. Our findings not only demonstrate enhanced synthetic utility of the photomediated ring contraction and shed light on mechanistic details but may also offer valuable guidance for understanding wavelength-dependent reactivity for related photochemical systems.

This research not only advances the synthetic utility of photomediated ring contraction but also sheds light on the mechanistic and photophysical aspects of photochemical systems. This work was jointly done between the Sarpong group, colleagues from Merck and Abbvie, and our group.

Published manuscript in the Journal of the American Chemical Society:
https://pubs.acs.org/doi/10.1021/jacs.3c13982

New paper out: Ultrafast formation of topological defects in a 2D charge density wave
Jan 8 2024

Topological defects play a key role in nonequilibrium phase transitions, ranging from birth of the early universe to quantum critical behavior of ultracold atoms. In solids, transient defects are known to generate a variety of hidden orders not accessible in equilibrium, but how defects are formed at the nanometer length scale and femtosecond timescale remains unknown. In this work, we discovered the sub-picosecond formation of 1D topological defects in a two-dimensional charge density wave using ultrafast electron diffraction. We discovered a dual-stage growth of 1D domain walls which takes place within 1 ps which is mediated by nonthermal lattice vibrations. This work constitutes the first visualization of topological defect formation process in the femtosecond timescale. Our work provides a framework for ultrafast engineering of topological defects based on selective excitation of collective modes, opening new avenues for dynamical control of nonequilibrium phases in correlated materials.

This work was done in collaboration with researchers from Shanghai Jiao Tong University, Brookhaven National Laboratory, ShanghaiTech University, University of Amsterdam and UCLA.

Press release by the College of Chemistry:
https://chemistry.berkeley.edu/news/birth-of-topological-defects-in-charge-density-wave

The paper is now published at Nature Physics:
https://www.nature.com/articles/s41567-023-02279-x

An associated News & Views Article has been published by Isabella Gierz:
https://www.nature.com/articles/s41567-023-02285-z

Open Access pre-print available here:
https://arxiv.org/abs/2211.05748

Michael contributed to DOE Basic Research Needs Workshop
Jan 7 2024

Today the workshop report of the Basic Research Needs (BRN) Workshop on Laser Technology was released. This workshop was co-organized by DOE, DOD and NSF, and held in Fall 2023. Michael contributed as scientific panel member to the workshop discussing needs for advanced laser technologies in ultrafast science. The full report can be read here:
https://science.osti.gov/-/media/ardap/pdf/2024/Laser-Technology-Workshop-Report_20240105_final.pdf

Technical Development Award for Michael
Nov 10 2023

The Japanese Society of Vacuum and Surface Science (JSVSS) presented a technical development award for the development of the XUV-SHG technique to Michael for the highly successful implementation of this technique at the japanese free-electron laser SACLA.

New pre-print: A solid-state high harmonic generation spectrometer with cryogenic cooling
Sep 7 2023

Solid-state high harmonic generation spectroscopy (sHHG) has emerged as a pivotal technique for delving into electronic structure, symmetry, and dynamics in condensed matter systems. In our latest manuscript, we introduce an advanced cryogenic sHHG spectrometer, uniquely designed with a vacuum chamber and a closed-cycle helium cryostat. With the aid of an in situ temperature probe, we’ve ascertained that the sample interaction region maintains cryogenic temperatures even during the application of high-intensity femtosecond laser pulses, which are responsible for generating high harmonics. Our approach paves the way for temperature-dependent sHHG measurements down to a few Kelvin. Such advancements in sHHG spectroscopy present a novel tool for investigating phases of matter that manifest at low temperatures, an area of particular intrigue for highly correlated materials.

Pre-print is available here: https://arxiv.org/abs/2309.01049

Welcome Prof. Dean Smith
Aug 28 2023

Our group welcomes Prof. Dean Smith from the University of Nevada, Las Vegas. Dean is a frequent collaborator of our group on applications of high pressure science probed with nonlinear spectroscopies and will be visiting our group for the next year.

Michael receives DOE Early Career Award
Aug 4 2023

We are excited to share that Michael was among this year’s awardees of the prestigious DOE Early Career Research Program Award. In this 5-year award on the topic “Ultrafast mechanisms of chirality control in electronic materials” we will use new capabilities of our attosecond instrument in combination with facilities at SLAC to study control mechanisms of chiral order in quantum materials.

College of Chemistry press release:
https://chemistry.berkeley.edu/news/michael-zuerch-receives-prestigious-doe-early-career-research-program-award

Press release from the Department of Energy can be found here:
https://science.osti.gov/early-career

Group writing retreat at Point Reyes
Jul 27 2023

With a large part of the group we did a 2-day writing retreat at the UC Berkeley Field Station in Point Reyes National Seashore. Focus besides discussing science and catching up about different projects was on writing a comprehensive group manual that we hope will serve our group well in the future.

New paper out: Detecting driving potentials at the buried SiO2 nanolayers in solar cells bychemical-selective nonlinear X-ray spectroscopy
Jul 17 2023

We are excited to share our newest paper where we selectively examine an asymmetric potential in the buried layer of solar cell devices by means of nonlinear X-ray spectroscopy. This collaborative work under lead of Walter Drisdell (LBNL) was published in Applied Physics Letters.

In this work, we systematically investigate Al/LiF/SiO2/Si, TiO2/SiO2/Si, and Al2O3/SiO2/Si multilayer structures by probing around the Si L edge using second-harmonic XUV spectroscopy. We directly observe existence of the band bending effect in the SiO2 nanolayer, buried in the heterostructures. The results demonstrate high sensitivity of the method to the asymmetric potential that determines performance of functional materials for photovoltaics or other optoelectronic devices.

This work was done in collaboration with researchers from the University of Tokyo, the University of Melbourne, UC Berkeley/LBNL, and the University of Nevada Las Vegas. The measurements were conducted at the SACLA free-electron laser at RIKEN in Japan.

Open-access to the research paper at Applied Physics Letters:
https://pubs.aip.org/aip/apl/article/123/3/031602/2902887/Detecting-driving-potentials-at-the-buried-SiO2

Welcome Ali
Jun 1 2023

We welcome Ali Elhadi as NSF-REU summer student. Ali is majoring in physics at the University of Minnesota and will work on solid-state high harmonic generation spectroscopy this summer.

Staib Instruments Best Oral Presentation Award for Alfred
Apr 30 2023

Congratulations to Alfred for being awarded the Staib Instruments Best Oral Presentation Award for his talk “Ultrafast Formation of Topological Defects in a 2D Charge Density Wave” at the recent MRS Spring Meeting!

New paper out: Probing lithium mobility at a solid electrolyte surface
Apr 29 2023

We are excited to share our newest paper where we study surface lithium ion mobility in a solid-state electrolyte using extreme ultraviolet second-harmonic generation spectroscopy (XUV-SHG). This work was published in Nature Materials.
In this work, we investigate a prototypical solid-state electrolyte using linear and nonlinear extreme-ultraviolet spectroscopies. Leveraging the surface sensitivity of extreme-ultraviolet-second-harmonic-generation spectroscopy, we obtained a direct spectral signature of surface lithium ions, showing a distinct blueshift relative to bulk absorption spectra. First-principles simulations attributed the shift to transitions from the lithium 1 s state to hybridized Li-s/Ti-d orbitals at the surface. Our calculations further suggest a reduction in lithium interfacial mobility due to suppressed low-frequency rattling modes, which is the fundamental origin of the large interfacial resistance in this material. Our findings pave the way for new optimization strategies to develop these electrochemical devices via interfacial engineering of lithium ions.

This work was done in collaboration with researchers from UC San Diego, University of Tokio, Argonne National Laboratory, UC San Diego, and the University of Nevada Las Vegas. The measurements were conducted at the SACLA free-electron laser at RIKEN in Japan.

Open-access to the research paper at Nature Materials:
https://www.nature.com/articles/s41563-023-01535-y

College of Chemistry press release:
https://chemistry.berkeley.edu/news/search-nonflammable-lithium-battery-technology

Congrats to Sheng-Chih!
Mar 22 2023

Hearthy congratulations to Sheng-Chih for passing his qualification exam!

Welcome to new undergraduate researchers
Mar 1 2023

We are excited to welcome new undergraduate researchers to our group. Welcome to Ann (Chem), Shaneil (DOE SULI Fellow) and Andy (EECS/Physics)!

New paper out: Emerging ultrafast techniques for studying quantum materials
Feb 15 2023

We are excited to share that a detailed review of our primary work area, namely the study of non-equilibrium phenomena in quantum matter using novel ultrafast spectroscopies, has been published in Nature Reviews Materials.

The field of quantum materials and emerging phenomena has developed with an ever-accelerating pace. Most of the research in this broad field uses traditional control knobs such as temperature, pressure, chemical substitution, and static electric or magnetic fields to tweak materials to explore the phase space offering access to potentially new phenomena. In the past decade, ultrafast techniques down to the femtosecond timescale — such as photoemission, scattering, and optical spectroscopies — have added the time-coordinate as a new dimension for understanding and engineering properties of quantum materials out of equilibrium. Despite significant progress, there remain a host of open questions that will require detailed understanding of the nonequilibrium response of quantum materials to enable future applications in areas such as clean energy production, energy storage, and quantum computation and communication.

Our review focuses on novel ultrafast spectroscopies that have only been recently developed for investigating condensed matter systems (attosecond transient absorption spectroscopy (ATAS), solid-state high harmonic generation (sHHG), and extreme ultraviolet-second harmonic generation (XUV-SHG)). We discuss their potential applications to study emerging phenomena in quantum materials and focus on the standpoint of open questions in quantum materials as well as the unique observables and capabilities these methods can offer to address them.

The bulk of the literature search, review and writing has been done during a writing retreat in summer 2022 and I am particularly excited that all co-authors are group members who all contributed significantly to this work.

Our paper was published in Nature Reviews Materials:
https://www.nature.com/articles/s41578-022-00530-0

Michael to lead California Interfacial Science Institute
Jan 30 2023

We are excited to announce that our effort that started 2 years ago as the California Interfacial Science Initiative has received new funding through the UC MRPI program. With this $1.1M in direct funding we will extend the capacity and become the California Interfacial Science Institute. In the next 3 years we will continue our work on studying chemically-relevant interfaces by combination of theory and experiment and we now include additional leading researchers from UCLA and UC Santa Barbara. We also will establish a novel undergraduate research fellowship for conducting summer research in CISI affiliated laboratories.
Additional details can be found in the College of Chemistry press release here:
https://chemistry.berkeley.edu/news/uc-funds-new-california-interfacial-science-institute

New paper out: Coherent Phonons in Antimony: An Undergraduate Physical Chemistry Solid-State Ultrafast Laser Spectroscopy Experiment
Nov 17 2022

We are excited to see our latest paper on “Coherent Phonons in Antimony: An Undergraduate Physical Chemistry Solid-State Ultrafast Laser Spectroscopy Experiment” published in the ACS Journal of Chemical Education. This paper in chemical education discusses in deep detail an ultrafast spectroscopy experiment that we developed for our undergraduate teaching laboratory at Berkeley. In the experiment, the students measure coherent phonons in antimony using the output of a femtosecond laser oscillator which they also characterize in the time domain. This lab experiment that is usually done by juniors and seniors in the Chemistry curriculum has since its inauguration become one of the favorite experiments that students in this course do. We hope it will spark excitement for research using ultrafast methods in their future careers.

This work was done in collaboration with Steve Leone and Anne Baranger.

Our open access paper is now published in the Journal of Chemical Education:
https://pubs.acs.org/doi/full/10.1021/acs.jchemed.2c00816

New pre-print: Ultrafast formation of topological defects in a 2D charge density wave
Nov 15 2022

Topological defects play a key role in nonequilibrium phase transitions, ranging from birth of the early universe to quantum critical behavior of ultracold atoms. In solids, transient defects are known to generate a variety of hidden orders not accessible in equilibrium, but how defects are formed at the nanometer lengthscale and femtosecond timescale remains unknown. In this work, we discovered the sub-picosecond formation of 1D topological defects in a two-dimensional charge density wave using ultrafast electron diffraction. We discovered a dual-stage growth of 1D domain walls which takes place within 1 ps which is mediated by nonthermal lattice vibrations. This work constitutes the first visualization of topological defect formation process in the femtosecond timescale. Our work provides a framework for ultrafast engineering of topological defects based on selective excitation of collective modes, opening new avenues for dynamical control of nonequilibrium phases in correlated materials.

This work was done in collaboration with researchers from Shanghai Jiao Tong University, Brookhaven National Laboratory, ShanghaiTech University, University of Amsterdam and UCLA.

Pre-print available here:
https://arxiv.org/abs/2211.05748

Welcome Prof. Craig Schwartz
Oct 15 2022

Our group welcomes Prof. Craig Schwartz from the University of Nevada, Las Vegas. Craig is a long-term collaborator of our group on XUV and FEL science and will be visiting our group for the next year.

Our work got featured on JPCL front cover
Oct 6 2022

We are excited to find the artwork for Lars’ most recent paper on the front cover of the Journal of Physical Chemistry Letters!

In addition, FERMI/ELETTRA published a TOP Story on their website about our work: https://www.elettra.eu/science/top-stories/intense-x-ray-radiation-changes-how-light-and-matter-interact.html

New paper out: Signatures of multi-band effects in high-harmonic generation in monolayer molybdenum disulfide
Oct 4 2022

We are excited to see our latest paper on “Signatures of multi-band effects in high-harmonic generation in monolayer molybdenum disulfide” appear in Physical Review Letters. In this joint experimental and theoretical work on solid-state high-harmonic generation (HHG), we illustrate that the polarization properties of the harmonics encode not only the dynamical symmetry properties of the crystal and laser field system, but also material-specific properties such as the vectorial character of the transition dipole moments from different valence-conduction-band pairs. Importantly, we conduct experiments on monolayer materials which enables us to show that angular spectral shifts of the harmonic emission stem from multiband contributions instead of bulk propagation effects.

This work was done in collaboration with researchers from the Louisiana State University, Friedrich Schiller University Jena, and Yale University.

Our open access paper is now published in Physical Review Letters:
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.147401

New paper out: Saturable absorption of free-electron laser radiation by graphite near the carbon K-edge
Sep 27 2022

We are excited to see Lars’ first paper on “Saturable absorption of free-electron laser radiation by graphite near the carbon K-edge” published. In this experiment, we study in a single experiment supported by state-of-the-art numerical simulations how intense femtosecond X-ray free-electron laser pulses induce two different nonlinear responses, saturable absorption (SA) and two-photon absorption (TPA), depending on intensity. We find that SA and TPA are competing processes in the X-ray regime and the relative transition strengths determine at which intensities TPA becomes dominant over SA which is a material-specific property. Our results reveal the competing contributions of distinct nonlinear material responses to spectroscopic signals measured in the X-ray regime, demonstrating an approach of general utility for interpreting FEL spectroscopies. This opens new routes for dynamically probing properties of matter.

This work was done in collaboration with researchers from the Saykally group at UCB, LBNL, U of Texas Rio Grande Valley, UC San Diego, and FERMI. The experiments were conducted at the free-electron laser facility FERMI in Italy.

Our open access paper was now published in the Journal of Physical Chemistry Letters and was selected as Editor’s pick:
https://pubs.acs.org/doi/10.1021/acs.jpclett.2c01020

Michael joins International Program Committee of ATTO
Jul 18 2022

During the 8th ATTO Conference in Orlando, FL, was inducted to the International Program Committee of ATTO which is one of the most important conferences in the field of attosecond science. In this role Michael will contribute to shaping this important conference in the years to come.

Welcome Jackson!
Jun 2 2022

We are excited to welcome Jackson McClellan who joins us for the summer through the NSF-REU program. Jackson majors in Physics at the Ohio State University and will work over the summer on disentangling complex X-ray diffraction signatures of a photoexcited solid-state electrolyte.

Nadia is awarded Departmental Citation
May 18 2022

Congratulations to Nadia! She got awarded the Departmental Citation in Chemistry which is one of the highest honors in the College of Chemistry for undergraduates and she also graduated with honors. Photo shows her receiving the award at the 2022 Commencement.

First writing retreat
May 18 2022

Under the motto “Get it done” we did our first group writing retreat with part of the group. We spent 2 days reading, writing and discussing research in the beautiful Napa Valley at the Napa River to catch up on a writing project we had been trying to work on for a while. It was a really productive two days and we also got to enjoy the start of summer.

Jacob awarded Arnold O. Beckman Postdoctoral Fellowship
May 6 2022

We are extremely excited to share that Jacob got the prestigious and highly competitive Arnold O. Beckman Postdoctoral Fellowship awarded. This is absolutely awesome news and a very well deserved honor based on his past accomplishments at Yale but also in consideration of a highly competitive research proposal he put forward for his research in our group. Some more information here: https://www.beckman-foundation.org/latest-news/2022-aob-postdoctoral-fellows/
Congratulations Jacob!

Welcome Jacob!
Apr 25 2022

We are excited to welcome Jacob Spies as post-doctoral fellow to the Zuerch Lab! Jacob finished his PhD at Yale earlier this year, where he did research in the Schmuttenmaer/Brudvig groups. He will join our efforts in solid-state high harmonic generation and THz spectroscopy.

New paper out: Separating nonlinear Optical Signals of a Sample from High Harmonic Radiation in a Soft X-ray Free Electron Laser
Apr 11 2022

In this paper we report a new ellipsometry method for soft X-ray SHG to suppress the contribution of second-harmonic radiation from the light source. Through measurements of a GaAs(100) crystal, we demonstrate that pure SHG signals can be obtained for the horizontally polarized component. The present method is generally applicable regardless of the incident photon energy and hence the absorption edge of the targeted materials. If combined with optical filters blocking the second-harmonic radiation and equipped with soft X-ray phase shifters, the method allows one to obtain further information from SHG signals such as tensor components of second-order nonlinear susceptibility.

This method paper was published under the leadership of our collaborators from the University of Tokyo.

Our paper was now published in e-Journal of Surface Science and Nanotechnology:
https://www.jstage.jst.go.jp/article/ejssnt/20/1/20_2022-002/_arti

ACS Spring Meeting 2022
Apr 9 2022

We are excited to be finally able to do in-person representations of our research at scientific conferences. Finn, Bailey and Nadia were the first of our group to venture out and present their work at the ACS Spring Meeting in 2022 in March in San Diego!

Congratulations Bailey!
Mar 19 2022

Bailey passed her qualification exam with flying colors! We are very excited about this progress. Deserving a break from learning and the lab, Bailey is now headed next to ACS Spring Meeting in San Diego where she will present on her latest work on solid-state high harmonic generation.

Nadia leading implementation of new scanning electron microscope
Mar 15 2022

A new scanning electron microscope from ZEISS has been installed in our physical chemistry instructional labs. Michael has been leading establishing the partnership with ZEISS over the last few years that led to this opportunity to enhance instruction and research for undergraduates and graduate students at Berkeley. Since the installation of the instrument last Fall, Nadia has been working towards implementing the instrument in instruction and successfully used it for her own research. A news release of the College of Chemistry can be found here:
https://chemistry.berkeley.edu/news/new-microscope-technology-energizes-undergraduate-research

New paper out: Light-induced dimension crossover dictated by excitonic correlations
Feb 18 2022

We are very excited about this work being published with Alfred as shared-first author!

An excitonic insulator is an elusive state of matter that emerges following the Bose-Einstein condensation of excitons. 1T‑TiSe2 is one of very few candidates for an excitonic insulator, but its excitonic condensation occurs concurrently with a charge-density-wave (CDW) transition, sharing the same critical temperature of ~200 K. The relationship between excitonic correlation and CDW instability hence remains controversial. The question on which mechanism drives the phase transition has slipped into a chicken-and-egg problem despite more than forty years of debate.

A global team of researchers in China and the U.S. tackled this impasse by studying how the competing excitonic and CDW ground states responds to perturbation by a femtosecond laser pulse. The key finding is that photoexcitation turns an originally three-dimensional CDW transiently into a two-dimensional CDW. Importantly, this dimension reduction does not occur unless bound pairs of electrons and holes are broken, suggesting that excitonic correlations maintain the out-of-plane CDW coherence. These findings not only shed new light on the role of excitonic correlation in 1T‑TiSe2, but also demonstrate how optical manipulation of electronic interaction enables controlling the dimensionality of broken-symmetry order. These findings pave the way for realizing other emergent states in strongly correlated systems.

This work was co-led with Shanghai Jiao Tong University professors Dao Xiang and Jie Zhang, and UC Los Angeles professor Anshul Kogar.

Our paper was now published in Nature Communications:
https://www.nature.com/articles/s41467-022-28309-5

College of Chemistry press release with additional discussion:
https://chemistry.berkeley.edu/news/electronic-crystal-turned-flat

New paper out: High-Harmonic Generation from Resonant Dielectric Metasurfaces Empowered by Bound States in the Continuum
Feb 2 2022

Optical bound states in the continuum (BICs) underpin the existence of strongly localized waves embedded into the radiation spectrum. In this work, we bring the concept of BICs to the field of high-harmonic generation and employ resonant dielectric metasurfaces to generate efficiently optical harmonics up to the 11th order. We design BIC-resonant metasurfaces with a broken in-plane symmetry for the lower harmonics and then observe a transition to the nonlinear regime for higher harmonics. Our approach bridges the fields of perturbative and nonperturbative nonlinear optics on the subwavelength scale.
This work was led by researchers from the Australian National University in collaboration with researchers from Jena University and ITMO University.
Our paper was now published in ACS Photonics:
https://pubs.acs.org/doi/abs/10.1021/acsphotonics.1c01511

New pre-print: Signatures of multi-band effects in high-harmonic generation in monolayer molybdenum disulfide
Dec 24 2021

We are excited to share our latest pre-print on “Signatures of multi-band effects in high-harmonic generation in monolayer molybdenum disulfide”. In this joint experimental and theoretical work on solid-state high-harmonic generation (HHG), we illustrate that the polarization properties of the harmonics encode not only the dynamical symmetry properties of the crystal and laser field system, but also material-specific properties such as the vectorial character of the transition dipole moments from different valence-conduction-band pairs. Importantly, we conduct experiments on monolayer materials which enables us to show that angular spectral shifts of the harmonic emission stem from multiband contributions instead of bulk propagation effects.

This work was done in collaboration with researchers from the Louisiana State University, Friedrich Schiller University Jena, and Yale University.

Pre-print available here:
https://arxiv.org/abs/2112.13032

New pre-print: Saturable absorption of free-electron laser radiation by graphite near the carbon K-edge
Dec 14 2021

We are excited to share our latest pre-print on “Saturable absorption of free-electron laser radiation by graphite near the carbon K-edge”. In this experiment, we study in a single experiment supported by state-of-the-art numerical simulations how intense femtosecond X-ray free-electron laser pulses induce two different nonlinear responses, saturable absorption (SA) and two-photon absorption (TPA), depending on intensity. Our data suggests that SA and TPA are competing processes in the X-ray regime and the relative transition strengths determine at which intensities TPA becomes dominant over SA which is ultimately a material-specific property. Our results reveal the competing contributions of distinct nonlinear material responses to spectroscopic signals measured in the X-ray regime, demonstrating an approach of general utility for interpreting FEL spectroscopies. This opens new routes for dynamically probing properties of matter.

Congrats to Lars for his first submitted manuscript in the group.

This work was done in collaboration with researchers from the Saykally group at UCB, LBNL, U of Texas Rio Grande Valley, UC San Diego, and FERMI. The experiments were conducted at the free-electron laser facility FERMI in Italy.

Pre-print available here:
https://arxiv.org/abs/2112.12585

New paper out: Polarization-Resolved Extreme-Ultraviolet Second Harmonic Generation from LiNbO3
Dec 8 2021

We are excited to see our work on polarization-resolved second harmonic spectroscopy enabling element-resolved angular anisotropy investigations published. In LiNbO3 we directly resolve the Li ion displacement and its correlated action on the Nb-O bonds. This study constitutes the first observation of polarization-resolved SHG in the extreme ultraviolet (XUV) and we show that dipole-based SHG models used regularly in the optical regime allow predicting the SHG polarization in the in the XUV regime. The findings of this work pave the way for future angle and time-resolved XUV-SHG studies with elemental specificity in condensed matter systems.
This work as performed at the SACLA free-electron laser at Sping8/RIKEN in primary collaboration with UC San Diego, Argonne National Lab, LBNL and U Tokyo.
Our paper was now published in Physical Review Letters:
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.237402

Congrats Lars!
Oct 20 2021

Congratulations to Lars for passing his qualifying exam!

New paper out: Angstrom-Resolved Interfacial Structure in Buried Organic-Inorganic Junctions
Aug 24 2021

Charge transport processes at interfaces which are governed by complex interfacial electronic structure play a crucial role in catalytic reactions, energy storage, photovoltaics, and many biological processes. Here, the first soft X-ray second harmonic generation (SXR-SHG) interfacial spectrum of a buried interface (boron/Parylene-N)is reported. SXR-SHG shows distinct spectral features that are not observed in X-ray absorption spectra, demonstrating its extraordinary interfacial sensitivity. Comparison to electronic structure calculations indicates a boron-organic separation distance of 1.9±0.1 Å, wherein changes as small as 0.1 Å result in easily detectable SXR-SHG spectral shifts (ca. 100s of meV). As SXR-SHG is inherently ultrafast and sensitive to individual atomic layers, it creates the possibility to study a variety of interfacial processes, e.g. catalysis, with ultrafast time resolution and bond specificity.
This work was done in collaboration with researchers from the Saykally group at UCB, LBNL, UC San Diego, SLAC, and FERMI. The experiments were conducted at the free-electron laser facility FERMI in Italy.
Our paper was now published in Physical Review Letters:
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.096801

New paper out: Extreme Ultraviolet Second Harmonic Generation Spectroscopy in a Polar Metal
Jul 29 2021

In this work, we utilize XUV-SHG spectroscopy to investigate the polar metal phase of LiOsO3, where the coexistence of polarity and metallicity is unexpected since the itinerant conducting electrons in metals are expected to screen out long-range electrostatic forces that typically stabilize a permanent polarization. This is one of the first uses of nonlinear X-ray spectroscopy to investigate a material across a phase transition. A sensitivity to broken inversion symmetry appears above the Li K-edge, with theory showing how the spectrally-resolved SHG varies with Li-displacement. As the first demonstration of XUV-SHG spectroscopy around a phase transition, these results pave the way for using nonlinear XUV methods to investigate broken symmetry from an element-specific perspective.

Congratulations to Emma for her first author paper, and Angelique and Can for their first paper in the group. Also, we are excited for Clarisse’ first paper, who contributed to this work during her NSF-REU visit last summer.

This work was done in collaboration with researchers from LBNL, UC San Diego, Argonne National Laboratory, Penn State, and the University of Tokio. The experiments were conducted at the free-electron laser facility SACLA in Japan.

Our paper appeared in Nano Letters (open access) and was selected as cover featured article:
https://pubs.acs.org/doi/10.1021/acs.nanolett.1c01502
College of Chemistry news release:
https://chemistry.berkeley.edu/news/uc-berkeley-researchers-illuminate-material-complexity-nonlinear-x-ray-spectroscopy

Group retreat to Yosemite
Jul 22 2021

We had our first retreat as a group and went hiking two days in Yosemite National Park. Giant Sequoias, Glacier Point and several waterfalls were explored. Despite 103 degrees, it has been a very memorable retreat.

Michael is awarded the 2021 Fresnel Prize by the European Physical Society (QEOD)!
Jun 22 2021

Michael was awarded the 2021 Fresnel Prize by the European Physical Society – Quantum Electronics and Optics Division in the “fundamental research” category “for outstanding contributions to the field of ultrafast condensed-matter science and for the application of linear and nonlinear X-ray spectroscopies to the investigation of quantum phenomena. The Fresnel Prize is awarded every 2 years to a researcher 35 years or younger, one each in the areas of fundamental and applied research. The award ceremony took place virtually during the CLEO Europe conference.

College of Chemistry News Release:
https://chemistry.berkeley.edu/news/michael-zuerch-receives-award-quantum-electronic-and-optics-research

New paper out: Table-top extreme ultraviolet second harmonic generation
May 19 2021

Nonlinear optical spectroscopies have significantly advanced the understanding of chemical dynamics at surfaces. One limitation in the optical regime has been the constrain to valence dynamics making probing in complex chemical environments and attributing dynamics to specific atomic species difficult. We now demonstrate second harmonic generation (SHG) on titanium in the extreme ultraviolet (XUV) using a femtosecond table-top laser. We show that the observed XUV-SHG emission is specific to the inversion-symmetry broken surface of titanium. These findings open new possibilities to study chemical dynamics at surfaces and buried interfaces from the viewport of a specific atomic species.

In collaboration with Institut Polytechnique de Paris, UC San Diego, SLAC National Accelerator Laboratory, and the Friedrich Schiller University Jena.

Congratulations to Emma for her first shared-first author paper and to Lars for his first paper in the group!

Our paper appeared in Science Advances and was selected as cover featured article:
https://advances.sciencemag.org/content/7/21/eabe2265
Press release from the College of Chemistry:
https://chemistry.berkeley.edu/news/berkeley-researchers-demonstrate-new-technique-surface-sensitive-second-harmonic-generation

Welcome Nadia, Finn, Sophia, William & Douglas
Apr 23 2021

We are so excited to welcome several new group members starting April and May 2021! Nadia Berndt joins us as an undergraduate researcher working on time-resolved spectroscopy on encapsulated monolayer TMDC nano discs. Finn Kohrell (Friedrich Schiller University Jena, Germany) is a visiting student researcher funded by the German Academic Exchange Service (DAAD)  conducting research for his Master thesis on non-equilibrium dynamics in the superconducting state of 2D TMDCs at low temperatures for the next year. Sophia Fang (MIT) joins us for the summer as NSF-REU student and will work on attosecond pulse generation and dynamics. William Alexander is a freshman in Chemistry and Entrepreneurship and joins us as undergraduate researcher exploring new ways for applying virtual reality in lab instruction and laser lab operation. Last but not least, Douglas Heine (Michigan State University) joins us this summer as NSF-REU student working on simulating strong-field excitations in two-dimensional semiconductors.

Michael appointed to editorial board at Nanoscale Research Letters
Apr 5 2021

Michael got appointed to the editorial board at Nanoscale Research Letters (NRL) at SpringerOpen which is part of Springer-Nature. NRL is a peer-reviewed open access journal focusing on nanoscale research in physics, materials science, biology, chemistry, and engineering.

Congratulations Emma!
Mar 23 2021

We are so excited that Emma got awarded the NSF Graduate Fellowship. Hearthy congratulations!

New paper out: Attosecond state-resolved carrier motion in quantum materials probed by soft x-ray XANES
Mar 13 2021

Recent developments in attosecond technology led to table-top x-ray spectroscopy in the soft x-ray range, thus uniting the element- and state-specificity of core-level x-ray absorption spectroscopy with the time resolution to follow electronic dynamics in real-time. In this new paper we describe recent work in attosecond technology and investigations into materials such as Si, SiO2, GaN, Al2O3, Ti, and TiO2, enabled by the convergence of these two capabilities. We showcase the state-of-the-art on isolated attosecond soft x-ray pulses for x-ray absorption near-edge spectroscopy to observe the 3d-state dynamics of the semi-metal TiS2 with attosecond resolution at the Ti L-edge (460 eV). We describe how the element- and state-specificity at the transition metal L-edge of the quantum material allows us to unambiguously identify how and where the optical field influences charge carriers. This precision elucidates that the Ti:3d conduction band states are efficiently photo-doped to a density of 1.9 × 1021 cm−3. The light-field induces coherent motion of intra-band carriers across 38% of the first Brillouin zone. Lastly, we describe the prospects with such unambiguous real-time observation of carrier dynamics in specific bonding or anti-bonding states and speculate that such capability will bring unprecedented opportunities toward an engineered approach for designer materials with pre-defined properties and efficiency. Examples are composites of semiconductors and insulators like Si, Ge, SiO2, GaN, BN, and quantum materials like graphene, transition metal dichalcogens, or high-Tc superconductors like NbN or LaBaCuO. Exiting are prospects to scrutinize canonical questions in multi-body physics, such as whether the electrons or lattice trigger phase transitions.

Congratulations to Emma for her first paper in the group!

Our paper appeared in Applied Physics Reviews and was selected as AIP featured article:
https://aip.scitation.org/doi/10.1063/5.0020649
In addition a more accessible AIP SciLight appeared for this article:
https://aip.scitation.org/doi/10.1063/10.0003826

Michael is awarded the Science and Engineering Research Grant from the W. M. Keck Foundation!
Feb 11 2021

A joint research project with the Bediako Group will receive $1M funding by the W. M. Keck Foundation to study novel 2D supercrystals and their magnetic properties at and far from equilibrium.

Welcome Richard!
Jan 26 2021

We are excited to welcome Richard Hollinger as post-doc to the Zuerch Lab! Richard completed his PhD at the Friedrich Schiller University and was awarded a Feodor Lynen Fellowship of the Alexander von Humboldt Foundation for his post-doc stay.

Michael to lead California Interfacial Science Initiative
Jan 16 2021

We are very excited to receive our first major grant funded by the Office of the President of the University of California within the Multicampus Research Programs and Initiative (MRPI). For the next 2 years, Michael will lead a team of researchers across the University of California to study the chemistry of liquids and solids on burried interfaces.

Here is the lay abstract for the project:
The world around us is governed by constant exchange of energy and particles. The internal structure at the interface between two media determines how phases interchange, how charge carriers exchange, and how media bind to one another. Therefore, understanding interfacial chemistry at a molecular level is of striking importance for a wide array of current challenges, such as clean water production, carbon dioxide capture, removal of plastics from water, clean energy production by photocatalysis, and energy storage in next generation solid-state batteries. Despite the importance, little is known about interfacial electronic and molecular structures, their dynamics, and how these lead to observed macroscopic properties and behaviors. The overarching goal of the California Interfacial Science Initiative (CISI) is to coordinate currently separate theoretical and experimental efforts studying interfaces across the University of California and leverage the combined expertise towards the creation of a world-leading center for interfacial science. During the pilot phase, multidisciplinary investigations will focus on two main topics: exploiting novel colliding planar liquid jets to study liquid-liquid interfaces investigating interfacial molecular dynamics relevant to CO2 capture and particle binding, and ionic charge transfer at solid-solid interfaces relevant to development of next generation batteries. The expertise for interfacial studies stems from first experiments on novel nonlinear X-ray spectroscopy that showed interfacial selectivity (UCB, LBNL) and a theory framework for nonlinear light-matter interactions (UCSD). CISI will bring together and consolidate these efforts by involving molecular level energy transfer theory (UCSC), interfacial engineering (UC-Merced) and quantum statistics calculation (LLNL). The multidisciplinary research team in the initiative will jointly develop advanced experimental techniques that enable studying these complex interfaces, which includes novel planar liquid jet technology, nonlinear optical and X-ray spectroscopies, and numerical models to simulate and understand interfacial dynamics.

New paper out: Polarization Dependent Excitation and High Harmonic Generation from Intense Mid-IR Laser Pulses in ZnO
Dec 26 2020

The generation of high order harmonics from femtosecond mid-IR laser pulses in ZnO has shown great potential to reveal new insight into the ultrafast electron dynamics on a few femtosecond timescale. In this collaborative work between groups from Jena University, TU Vienna and UC Berkeley, we report on the experimental investigation of photoluminescence and high-order harmonic generation (HHG) in a ZnO single crystal and polycrystalline thin film irradiated with intense femtosecond mid-IR laser pulses. The ellipticity dependence of the HHG process is experimentally studied up to the 17th harmonic order for various driving laser wavelengths in the spectral range 3–4 µm. Interband Zener tunneling is found to exhibit a significant excitation efficiency drop for circularly polarized strong-field pump pulses. For higher harmonics with energies larger than the bandgap, the measured ellipticity dependence can be quantitatively described by numerical simulations based on the density matrix equations. The ellipticity dependence of the below and above ZnO band gap harmonics as a function of the laser wavelength provides an efficient method for distinguishing the dominant HHG mechanism for different harmonic orders.
Our paper appeared in Nanomaterials:
https://www.mdpi.com/2079-4991/11/1/4

Welcome Lars!
Nov 13 2020

We extend a warm welcome to Lars Hoffmann who joins our lab this Fall as joint graduate student with the Gessner Group. Lars received his Masters degree from the Free University in Berlin and worked with Michael at the Fritz Haber Institute in Berlin for is M.Sc. thesis before coming to Berkeley. Lars will work on gas phase dynamics in molecules in the Gessner Lab at the Lawrence Berkeley National Laboratory.

Welcome Bailey!
Nov 2 2020

We are excited that Bailey Nebgen joins our lab this Fall as graduate student. She received her undergraduate degree from the University of Minnesota. Bailey will join our efforts on attosecond spectroscopy on quantum materials and THz spectroscopy.

Pre-Print: Direct observation of symmetry-breaking in a ferroelectric polar metal
Oct 15 2020

Check out our newest preprint on investigating inversion-breaking symmetry in a polar metal lithium osmate using nonlinear X-ray spectroscopy!
Ferroelectric materials containing a switchable spontaneous polarization in combination with metallicity, hence polar metals, have intriguing prospects for exotic quantum phenomena such as unconventional pairing mechanisms giving rise to superconductivity, topological spin currents, anisotropic upper critical fields, Mott multiferroics, and the wide range of applications arising from these phenomena. Our experimental approach using element-specific nonlinear X-ray spectroscopy provides direct access to the symmetry breaking properties exerted by the lithium atom in the unit cell and enables mapping of the dielectric environment. We also perform ab initio density functional perturbation theory (DFPT) calculations to understand the implications of our experimental finding and to validate our observation.
In collaboration with UC San Diego, Lawrence Berkeley National Lab, the Pennsylvania State University and Argonne National Lab. Measurements performed at the SPring-8 Angstrom Compact free electron LAser (SACLA).
Link to Arxiv manuscript:
https://arxiv.org/abs/2010.03134

Pre-Print: Table-top Nonlinear Extreme Ultraviolet Spectroscopy
Sep 15 2020

Our newest pre-print is out! In this work we demonstrate for the first time that we can perform second harmonic generation in the extreme ultraviolet at the titannium M-edge with a table-top instrument. This provides a new much more accessible route towards spectroscopy of surfaces and interfaces with elemental specificity. Emma’s first shared-first author paper in collaboration with the group of Tod Pascal at UCSD.
Link to the Arxiv manuscript:
https://arxiv.org/abs/2009.05151

Welcome Alfred!
Sep 1 2020

We are excited to welcome Alfred Zong as post-doctoral researcher to our group. Alfred did his undergraduate studies at Stanford and his PhD at the MIT. He is supported by the prestigous Miller Postdoctoral Fellowship. Alfred will join us studying fastest processes in correlated materials using attosecond diffraction spectroscopy.

Laser arrived!
Aug 9 2019

We are delighted to report that our ultrafast laser system arrived today in no less than 17 boxes. Many thanks to our effortless helpers on campus and the facility colleagues helping to get a temporary storage area prepared quickly. Quite some heavy lifting today, but totally worth it.

Welcome Ruoxu
Aug 8 2019

We welcome Ruoxu to our group as summer student. Ruoxu is starting her graduate research this Fall at Berkeley. She received her undergraduate degree from Grinnell College.

Zuerch Lab has moved
Aug 2 2019

We are excited to announce that the Zuerch Lab is moving from the Fritz Haber Institute in Berlin, Germany, to the University of California at Berkeley following Michael accepting an offer to join the Faculty at Berkeley in the College of Chemistry as Assistant Professor. Our new labs are under construction in the D-levels of Giauque Hall and the offices in the neighbouring Hildebrand Hall on the Berkeley Campus.

Paper on the Retrieval of the complex-valued refractive index of germanium near the M4,5 absorption edge published
Jun 1 2019

Our paper “Retrieval of the complex-valued refractive index of germanium near the M4,5 absorption edge” has been published in the Journal of the Optical Society of America B. In this work we show that the complex-valued index of refraction of germanium in the extreme ultraviolet (XUV) is measured by multi- angle reflectance of synchrotron radiation. The resulting index of refraction is higher resolution than previously measured values. It reveals new structures attributed to transitions from the 3d-core orbitals to the Σ5c,2 and the X5c,2 conduction bands. Additionally, we show that the problem of total external reflection, which renders multi-angle reflectance measurements insensitive to the complex-valued refractive index at grazing incidence, can be overcome by employing measurements at angles of incidence away from the critical angle.

Original link to the journal:
https://www.osapublishing.org/josab/abstract.cfm?uri=josab-36-6-1716

Paper on wavelength-scale ptychographic coherent diffractive imaging published
Feb 19 2019

Our paper “Wavelength-scale ptychographic coherent diffractive imaging using a high-order harmonic source”, which was the result of a collaboration between several Jena-based groups collaborating in a Forschergruppe in the State of Thuringia (2015 FGR 0094), has just been published in Scientific Reports. In this work, a full-field imaging resolution of 45 nm, corresponding to 2.5 wavelengths, was achieved using an advanced XUV source at the Institute of Applied Physics at FSU Jena. For better comparison of results in XUV imaging a Rayleigh-type criterion is used as a direct and unambiguous resolution metric for high-resolution table-top setup. This reliably qualifes this imaging system for real-world applications e.g. in biological sciences, material sciences, imaging integrated circuits and semiconductor mask inspection.

Original link to the journal:
https://www.nature.com/articles/s41598-019-38501-1

Perspective on single shot time-resolved microscopy using short wavelength table-top light sources published
Feb 13 2019

Our perspective “Towards single shot time-resolved microscopy using short wavelength table-top light sources” has been published in Structural Dynamics and was selected as featured publication. In this perspective, we present the current state of the art techniques for full-field imaging in the extreme-ultraviolet- and soft X-ray-regime which are suitable for single exposure applications as they are paramount for studying dynamics in nanoscale systems. We evaluate the performance of currently available table-top sources, with special emphasis on applications, photon flux, and coherence. Examples for applications of single shot imaging in physics, biology, and industrial applications are discussed.


Original link to the journal:
https://aca.scitation.org/doi/10.1063/1.5082686

Paper on differentiating carrier and phonon dynamics at the silicon L-edge by XUV transient absorption published
Jan 28 2019

Our paper on “Differentiating Photoexcited Carrier and Phonon Dynamics in the Δ, L, and Γ Valleys of Si(100) with Transient Extreme Ultraviolet Spectroscopy” has just been published by The Journal of Physical Chemistry. In this study, we prepared carrier populations in specific valleys in the band structure of silicon by tuning our narrow-band pump pulses in on the corresponding transition energies. We observe this specific excitation does not readily 1:1 imprint on the dynamics at the absorption edge. Using a BSE-DFT model, we find that besides the carrier population itself, contributions by excited phonon modes cause a perturbation of the core-hole transition probability that additionally modifies the observed transient XUV spectra.

Original link to the journal:
https://www.nature.com/articles/s41598-019-38501-1

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